The invention concerns a fuel filter insert and a fuel filter comprising a prefilter element and a main filter element as well as comprising a water separating unit.
DE 10 2008 048 228 A9 discloses a fuel filter with a fuel filter insert comprising a prefilter element and a main filter element that are arranged one behind the other in axial direction relative to the longitudinal axis of the fuel filter. The fuel prefiltered by the prefilter element is pumped by means of a fuel pump, arranged outside of the filter housing, to the main filter element.
U.S. Pat. No. 3,900,400 B discloses a fluid filter with a filter housing in which two filter elements are arranged one atop the other in the direction of the longitudinal axis of the fluid filter and can be exchanged independent of each other. Between the two filter elements, an inflow channel for the fluid is formed that is axially delimited by an end disc of a lower filter element and by a housing clamping plate supported on the end disc resiliently by a spring. By means of the housing clamping plate, the upper one of the two filter elements is brought into seal-tight contact on a housing cover of the filter housing.
EP 0 852 158 A1 discloses a fuel filter with two filter elements that are arranged fluidically one behind the other and are arranged one atop the other in the direction of the longitudinal axis of the fuel filter.
WO 2006/070221 A1 discloses a further fuel filter with a prefilter element and a main filter element which are arranged concentric relative to the longitudinal axis of the fuel filter.
Similar fuel filters are disclosed in DE 20 2006 004 527 U1 and EP 1 485 605 B1.
The known filter systems enable an effective removal of particulate contaminants contained in the fuel. However, in particular diesel fuel comprises in practice often a relevant water content that can cause damage to or malfunction of high pressure fuel injection systems or diesel engines.